Enhanced and device for controlling the power in an asymmetric soft handover condition

ABSTRACT

A method and a device for controlling a method for controlling the power in an asymmetric soft handover condition in a communication network, including at least two cells  
     each cell being served by a first type network device adapted to serve second type network devices in the respective cell. The method comprises:  
     temporarily adjusting (step S 3 ) a communication parameter of at least one second type network device  
     to set up and/or maintain the communication of the second type network device with the first type network device of at least one of said cells.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and a device forcontrolling the transmission power in an asymmetric soft handovercondition in a communication network including at least two cells.

BACKGROUND OF THE INVENTION

[0002] In mobile communication technologies like, e.g. UMTS (UniversalMobile Telecommunication System), base stations—so-called first typenetwork devices—serve a limited number of mobile users—so-called secondtype network devices—according to the current location of the users. Aslong as a user is in a cell area of certain base station, he can obtainmobile services from that base station. The overall performance and thequality of the service depends—among others—on propagation conditions,cell type, cell size, load distribution and on the power level of thevarious signal transmissions, particularly of the pilot signal providedby each base station.

[0003] The pilot signal transmitted by each base station carries a bitsequence or code known by the mobile stations. The bit sequence can bebase station and sector dependent. The power level of the pilot signalreceived by the mobiles is used by the mobile stations to measure therelative distance between different base stations that could be used forcommunication. Thus, the power level of the pilot signal of a basestation determines how far a mobile can “hear” the base stations; i.e.the power of the pilot signal is an indication to the mobile station ofits ability to successfully use the signal from that base station whichis transmitting that pilot signal.

[0004] In Code Division Multiple Access networks (WCDMA-Systems forexample) the cell selection, re-selection and the selection of theactive set of cells which are used for communication is based on therelative strength of the received pilot signal power (CPICH Ec/Io,wherein Ec/Io=chip energy to total interference spectral density) fromdifferent cells. Thus, the borders of a cell are determined by therelative strength of the pilot signal received from different cells.Hence, the power level of the pilot signal determines the pilot powercoverage, i.e. the area of the cell in which the pilot signal issufficiently powered to be properly decoded by the mobile stations.

[0005] In the CDMA-Systems tight and fast power control is an importantaspect, particularly on the uplink channel to avoid that one singleoverpowered mobile station blocks a whole cell. The solution is a fastclosed-loop power control. By this control, the base station performsfrequent estimates of the received Signal to Interference Ratio (SIR)and compares it to a target SIR. If the measured SIR is higher than thetarget SIR, the base station will command the mobile station to lowerthe power. If it is too low, it will command the mobile station toincrease its power. The closed loop power control will thus preventpower inbalance among all the uplink signals received at the respectivebase station.

[0006] Additionally, a slower Outer Loop Power Control (OLPC-function)is provided which adjusts the target SIR in the base station accordingto the needs of the individual radio link and aims at a constant targetquality, usually defined as a bit error rate (BER) or block error rate(BLER). As one would waste much power capacity if one would set thetarget SIR to the worst case, i.e. for high mobile speeds, the targetSIR floats around a minimum value that just fulfils the required targetquality. The target SIR will change as a function of time, speed and thepropagation environment of the mobile changes. When the Outer Loop PowerControl adjusts the target SIR in the respective base station, the fastclosed loop control will react correspondingly and bring the SIR-valuereceived in the associated base stations back to the target SIR value.

[0007] During a Soft Handover situation (SHO) a mobile station is in theoverlapping cell coverage area of two cells belonging to different basestations. The communications between mobile station and the basestations take place concurrently via two air interface channels downlinkfrom each base station separately. In uplink direction, the code channelof the mobile station is received from both base stations, but thereceived data is then routed to the associated radio network controller(RNC) for combining. Then, the RNC selects the better communicationbetween the two possible radio links, and this selection takes placeperiodically, i.e. every 10 to 80 milliseconds.

[0008] In WCDMA-systems base stations are not synchronized, which isdifferent to other current CDMA technologies and the synchronization ofa new radio link between a mobile station and the base station takesplace during the radio link set up procedure. The uplink synchronizationwill be achieved and maintained only if the base station can receive astrong enough signal from the mobile, i.e. if the transmission power ofthe mobile station is high enough. The transmission power of the mobile,is however, controlled by the power control of the “stronger” radiolink. In this application the stronger link is defined as radioconnection requiring less transmission power from the mobile, and theweaker link is defined as radio connection requiring more transmissionpower from the mobile. The “stronger” cell is defined to be the cellwith the stronger link, and the “weaker” cell is defined to be the cellwith the weaker link.

[0009] If the links in a soft handover area are strongly asymmetric, thetransmission power of the mobile station may not be high enough to reachthe other base station(s) where the link is weaker. This implies thatfor the cell included in the active set of cells and requiringsignificantly higher transmission power from the mobile, the uplinksynchronisation will not be achieved or maintained, and the link set upto establish a soft handover procedure or the maintaining of the softhandover will practically fail.

[0010] This applies to any communication system where the transmissionof a second type network devices (e.g. mobile) is received by more thanone first type network device (e.g. base station) to setup and/ormaintain a communication link but its transmission power cannot beadjusted individually to each first type network devices.

SUMMARY OF THE INVENTION

[0011] Therefore, the object underlying the invention resides inproviding an enhanced method and device for controlling the power in anasymmetric soft handover situation in a communication network.

[0012] This object is solved by a method for controlling the power in anasymmetric soft handover condition in a communication network, includingat least two cells

[0013] each cell being served by a first type network device adapted toserve second type network devices in the respective cell,

[0014] the method comprising:

[0015] temporarily adjusting (step S3) a communication parameter of atleast one second type network device

[0016] to set up and/or maintain the communication of the second typenetwork device with the first type network device of at least one ofsaid cells.

[0017] The above object is also solved by a device for controlling thepower in an asymmetric soft handover condition in a communicationnetwork, including at least two cells

[0018] each cell being served by a first type network device (BS1, BS2)adapted to serve second type network devices (MS) in the respectivecell,

[0019] the device comprising:

[0020] additional control means for temporarily adjusting acommunication parameter of at least one second type network device

[0021] to set up and/or maintain the communication of the second typenetwork device with the first type network device of at least one ofsaid cells.

[0022] In accordance with the invention, the communication between firstand second type network devices can be achieved and maintained even inan area where the cells are under strongly asymmetric conditions, andonly a relevant communication parameter, for example the transmissionpower of the second type network device in question will have to beadjusted temporarily, exactly when needed.

[0023] Preferably, the communication parameter adjusted in theadjustment step includes the transmission power of the second typenetwork device in question, so that the first type network devices,which serve the cells, remain unchanged.

[0024] Before adjusting the communication parameter in the adjustingstep, preferably, information is detected which indicates the linkquality of the second type network device in both cells (detecting stepS1), and then an asymmetry parameter is evaluated, said asymmetryparameter indicating the imbalance of the link quality in the servingcells (evaluating step S2). On the basis of this asymmetry parameter,the transmission power of the second type network device in question isadjusted, if the asymmetry parameter exceeds a first threshold value.

[0025] In a preferred embodiment of the invention, this object is solvedby a method for controlling the transmission power in an asymmetric softhandover condition in a mobile telecommunication network, including atleast two cells partly overlapping each other

[0026] each cell being served by a first type network device adapted toserve second type network devices in the respective cell,

[0027] radio links in the stronger cell requiring less transmissionpower and in the weaker cell requiring more transmission power from thesecond type network device,

[0028] the method comprising the following steps:

[0029] detecting information (step S1), said information indicating theradio link quality of the radio links between the second type networkdevice and the first type network device of the overlapping cells

[0030] evaluating a asymmetry parameter in the overlapping cell area(step S2) on the basis of the information gained in the detecting step(S1), said asymmetry parameter indicating the imbalance of the linkquality in the overlapping cells

[0031] temporarily increasing (step S3) the transmission power of saidsecond type network device

[0032] if the second type network device enters the overlapping cellarea from the stronger cell and

[0033] if the asymmetry parameter evaluated in step S2 exceeds a firstthreshold value,

[0034] to set up and/or maintain an uplink synchronization with thefirst type network device of the weaker cell.

[0035] In a preferred embodiment, the above object is also solved by adevice for controlling the transmission power in an asymmetric softhandover condition of a mobile telecommunication network, including atleast two cells (C1, C2) partly overlapping each other and participatingin the soft handover

[0036] each cell being served by a first type network device (BS1, BS2)adapted to serve second type network devices (MS) in the respectivecell,

[0037] a closed loop power control means controlling the transmissionpower of each second type network device in response to a comparison ofthe detected SIR-data (signal to interference ratio data) of its actualradio link, with a SIR-target value,

[0038] an outer loop power control means (OLPC) providing andactualizing the SIR-target value for the closed loop power controlmeans,

[0039] radio links in the stronger cell (C1) of said cells requiringless transmission power and radio links in the weaker cell (C2)requiring more transmission power from the second type network device,the device comprising the following steps:

[0040] detection means for detecting information, said informationindicating the radio link quality of the radio links between the secondtype network device (MS) and the first type network device (BS1, BS2) ofthe overlapping stronger cell (C1) and weaker cell (C2), respectively

[0041] evaluation means for evaluating a asymmetry parameter in theoverlapping cell area on the basis of the information gained from thedetecting means, said asymmetry parameter indicating the imbalance ofthe link quality in the overlapping stronger cell (C1) and weaker cell(C2),

[0042] additional control means for temporarily increasing thetransmission power of said second type network device

[0043] if the second type network device enters the overlapping cellarea from the stronger cell and

[0044] if the asymmetry parameter evaluated by the evaluation means,exceeds a first threshold value,

[0045] to set up and/or maintain an uplink synchronization with thefirst type network device of the weaker cell (C2).

[0046] Preferably, the link quality is represented—in accordance withthe invention—by the link power budget of the respective links.

[0047] In a soft handover situation, i.e. when a mobile station (secondtype network device) is in the overlapping cell coverage area of twoadjacent cells, the radio links of the mobile station to the basestation (first type network device) of the “stronger” cell needs lesstransmission power from the second type network device than in a weakercell.

[0048] If the mobile, i.e. the second type network device, is comingfrom the cell with the stronger link, i.e. from the cell transmittingthe common pilot channel at a comparatively high level, the methodaccording to the invention will establish the uplink synchronizationwith the first type network device of the weaker cell, thus implementingthe weaker link. However, the second type network is not necessarilycoming from the cell with the stronger link. If the second type networkdevice enters from the cell with the weaker link into the overlappingarea, the transmission power of the second type network device accordingto this invention is temporarily prevented from being lowered by thepower control of the strongest link—and not increased—so as to meet theconditions required for soft handover. Otherwise, the uplinksynchronization to the first network device of the stronger cell willsucceed, but then the new stronger link will control the transmissionpower of the second type network device and the original cell'ssynchronization will fail.

[0049] To overcome these drawbacks, the invention detects informationcharacterizing the radio link imbalance in the weaker cell and in thestronger cell. This information is used to evaluate an asymmetryparameter which is a measure of the radio link imbalance between themobile and the respective base stations being different, i.e.asymmetric. The enhanced power control of the invention then increasesthe transmission power of the respective mobile station respectivelyprevents it from being lowered by the power control of the strongestlink, in order to get resp. maintain a strong enough transmission signalfor the weaker radio link to reach and maintain the uplinksynchronisation of the signal emitted by that mobile station. Thus, inaccordance with the invention the base station in the weaker cell willestablish resp. maintain the synchronisation of the mobile stationduring soft handover, when the radio link is set up.

[0050] By the invention Soft Handover—an important feature of a WCDMAsystem—will be possible in strongly asymmetric overlapping cell areas.Only the mobile station in question increases respectively does notlower due to the power control of the strongest link the power, whereasa desensitisation of the respective base station of the strongest linkwould increase the transmission power of all mobile stations in thestronger cell. As the transmission power of the mobile station inquestion increases only temporarily, i.e. exactly when needed, theinvention is economically handling the power budget. Temporary asymmetryin soft handover, e.g. due to different cell load (noise rise) will behandled automatically and no extra margin needs to be reserved therefor.

[0051] Finally, the concept of the invention allows more design freedomin the network in so-called future auto tuning systems whichautomatically adjust the relative strength of received pilot power inthe cells. When the asymmetry in radio links in a SHO-area is notlimiting the auto tuning capabilities, these auto tuning features aresignificantly more valuable.

[0052] In accordance with the preferred embodiment of the invention, thetransmission power of the second type network device, i.e. the mobilestation increases only, if the asymmetry parameter evaluated exceeds afirst threshold value, and if additionally the mobile station enters theoverlapping cell area, which is the soft handover area, SHO-area.Preferably, the transmission power of a respective mobile stationresumes the original value or a different value, when the mobile stationleaves the overlapping cell area. The new value of the transmissionpower may be newly determined by the power control of the serving cell.

[0053] The asymmetry parameter, indicating the different quality ofradio links in the overlapping cells is dependent on different variablesor factors, among which are the CPICH power level difference, theCPICH-E_(c)/I_(o) difference, wherein E_(c)/I_(o) is the chip energy tototal interference spectral density; and the asymmetric uplinksensitivity established by mast head amplifiers if used. The differentinterference situation due to different cell loads is also relevant withregard to the asymmetry parameter also, the difference in requireduplink E_(b)/N_(o) may be taken into account for determining theasymmetry parameter with regard to the overlapping cells involved,E_(b)/N_(o) being the signal to interference ratio in the radio accessbearer of the radio links. One or more of these factors or variables maybe detected in accordance with the invention to evaluate an asymmetryparameter of the invention.

[0054] In accordance with the preferred embodiment of the invention,each first type network device of each of the overlapping cellsestimates the received Signal to Interference Ratio (SIR-value), i.e.for the stronger cell(s) and for the weaker cell(s), this SIR-valuedescribing the radio link quality between the second type network deviceand the respective first type network devices effectively andindividually. To evaluate the asymmetry parameter of the overlappingcells, an offset value ΔSIR is calculated. This offset value ΔSIR shouldbe calculated based on measurements (noise rise, Eb/No) and parameters(CPICH transmit power, MHA). ASIR itself could be the radio linkasymmetry parameter. The calculation will be done preferably in thenetwork radio controller.

[0055] To enhance the control of the transmission power of the secondtype network device the SIR-target value involved in the closed looppower control of said device is adjusted in response to the asymmetryparameter. If for example the ΔSIR-value is defining the asymmetryparameter and is added as an SIR-offset value when the second typenetwork device enters the SHO-area from the stronger cell, the closedloop power control will command the second type network device toincrease its transmission power. Thus, in accordance with the invention,the SIR-target value originally provided by the outer loop power control(OLPC) is increased by a respective SIR-offset value which correspondsto the asymmetry parameter, so that the fast closed loop power control,which individually commands the transmission power of the second typenetwork device, is working on an increased target and will thus commanda correspondingly higher transmission power. The SIR-target value willresume the original value defined by the outer loop power control OLPCwhen the weaker cell, i.e. the unbalanced cell is removed from theactive set of cells, or when the asymmetry condition is no longerexisting. In case the second type network device enters the SHO areafrom the weaker cell, the transmission power of the second type networkdevice is maintained at the current level instead of increased in orderto maintain the weaker link.

[0056] Preferably, the SIR-offset value is a constant value. Inaccordance with an alternative embodiment of the invention, theSIR-target value provided by the OLPC-function is increased by adding anSIR-offset value, and the resulting new SIR-target value is keptconstant as long as the asymmetry condition is present, or as long asthe asymmetry parameter exceeds a pre-given threshold value. Inaccordance with a third alternative embodiment of the invention, theminimum allowed SIR-target value is adjusted, preferably increased, toguarantee the required transmission power of second type network devicefor setting up and/or maintaining all links envolved in the softhandover.

[0057] All embodiments, which increase resp. maintain the SIR-targetvalue provided by the OLPC-function are based on the idea to temporarilyadjust the target value of the closed loop power control, and as thisclosed loop power control is executed at a rate of for example 1.5 kHz,this increase operates faster than any significant change of pathlosscould possibly happen. Once the asymmetry condition is over or theunbalanced, weak cell is removed from the active set of cells, theSIR-target value will resume its original value defined by the OLPCfunction and again being constantly updated by OLPC.

[0058] In the closed loop power control the respective first typenetwork device, i.e. the respective base station, performs frequentestimates of the received signal to interference ratio (SIR) andcompares it to the target SIR and this first type network device willcommand the second type network device, i.e. the mobile station, toadjust the power accordingly. This closed loop power control is veryfast (i.e. 1500 times per second) and prevents any power inbalance amongall the uplink signals received in the first type network device. Inthis context, the OLPC-function adjusts the target SIR set point in thefirst type network devices according to the needs of the individualradio link and aims at a constant quality, usually defined as a certaintarget bit error rate BER or block error rate BLER. The target SIR setpoint will change over time as the speed and the propagation environmentof the second type network device changes.

[0059] When the asymmetry parameter evaluated in the evaluation stepexceeds a pre-given first threshold value and thus requires temporarilyincreasing resp. maintaining the transmission power of the second typenetwork device located in the overlapping cell area, this adjustmentwill be realized—in accordance with one further preferred embodiment ofthe invention—by increasing the quality target of the strongest linksOuter Loop Power Control. The Outer Loop Power Control will increaseresp. maintain the SIR-target value for the respective second typenetwork device which is in soft handover condition. To resume theoriginal SIR-offset value, the quality target is changed to its originalvalue so that the OLPC-function commands the SIR-target value back tothe original. This adjustment of the SIR-target value is determined bythe react time of the OLPC-function, and is thus somewhat slower thanchanging the SIR-target value directly. However, this embodiment of theinvention allows the SIR-target value to be fully controlled by the OLPCfunction in the radio network control of the network during theseasymmetric soft handover situations and may result in a lower SIR-targetin the first type network devices participating in the soft handover,thus reducing the uplink interference.

[0060] The invention can be implemented either by directly modifying theSIR-target value of the uplink OLPC function in the radio networkcontroller or by reducing the error rate target (e.g. BLER or BER) ofthe transport channels within the particular radio resource controlconnection (RRC connection) during the soft handover situation. In anycase, the situation is properly resumed when the unbalanced link, i.e.the unbalanced cell is moved from the active set, e.g. when the softhandover situation between unbalanced radio links belonging to differentradio link sets is over.

[0061] In accordance with the invention, modifying the SIR-target valueof the uplink OLPC function may be done in two preferred ways:

[0062] increase the SIR-target value by an offset ΔSIR and keep theincreased value constant as long as the handover condition is presentresp. keep the SIR-target value constant in case the SHO area is enteredfrom the weakest cell;

[0063] increase the parameter minimum SIR-target of the uplink OLPCfunction to the current SIR-target+an offset value ΔSIR resp. maintainit, the current SIR-target being a time variable function in thisembodiment, and the offset ΔSIR being preferably the asymmetry parameterof the invention as evaluated in step S2.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The present invention will be more readily understood withreference to the accompanying drawings in which:

[0065]FIG. 1 shows the structure of a WCDMA-network;

[0066]FIG. 2 shows a soft handover situation for a mobile station;

[0067]FIG. 3 shows a diagram representing the change of SIR-target valueas a function of time in accordance with a preferred embodiment of theinvention; and

[0068]FIG. 4 shows a diagram illustrating the change of SIR-target valueas a function of time in accordance with a second embodiment of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0069] In the following, preferred embodiments of the invention aredescribed in more detail with reference to the accompanying drawings.

[0070] According to the invention, a procedure is provided toautomatically increase the transmission power of a mobile station in awideband code division multiple access system, if the mobile station isin a soft handover situation, said mobile being located in an area ofoverlapping cells.

[0071]FIG. 1 illustrates the basic structure of a WDMA-system, in whichbase stations BS1, BS2, BS3 each define an associated cell C1, C2, C3.Transmission links are provided from the base stations BS1, BS2, BS3 tothe Radio Network Controller RNC; data received in the base stations arerouted to the RNC for combining, for processing these data and forcontrolling the soft handover routines.

[0072] By each base station BS1, BS2, BS3 a pilot signal is emittedwhich carries a bit sequence or a code known by the mobile stations. Thebit sequence is base station dependent. The received power level of thepilot signal is used by the mobile stations to measure the relativedistance between different base stations that could be used forcommunication. Thus, the power level of the pilot signal of a basestation BS1, BS2, BS3 determines the area of the associated cell C1, C2,C3. In the WCDMA-system the cell selection, re-selection and theselection of the active set of cells which are used for communication isbased on the relative strength of the received pilot powerCPICH-E_(c)/I_(o), wherein E_(c)/I_(o) is the chip energy to totalinterference spectral density from different cells. Thus, the boardersof a cell are determined by the relative strength of the received pilotsignal from the associated base station. By changing the pilot powerlevel, the area of the base station cells can be changed.

[0073] Mobile stations are in a soft handover situation SHO when thepower of the pilot signals of two or more cells are within a predefinedwindow. If so, the respective cells “overlap” and form the overlappingcell area or soft handover area.

[0074]FIG. 2 illustrates soft handover for a mobile MS1 (second typenetwork device), this mobile being in the overlapping cell coverage areaof the two cells C1 and C2 belonging to different base stations BS1, BS2(first type network device). In a soft handover situation, thecommunications between the mobile station MS1 and the base station takeplace concurrently via two air interface channels from each base stationseparately. In downlink, the same signal is sent from BS1 and BS2 to themobile MS1 except for the power control demands. In uplink directionhowever, in soft handover the code channel of the mobile station MS1 isreceived from both base stations BS1 and BS2. The received data are thenrouted to the radio network controller RNC for further processing, andthe better radio link between the two possible connections is selectedwithin the RNC.

[0075] The uplink synchronization with the respective base station BS1,BS2 will be achieved and maintained if the base station can receive astrong enough transmission signal. The transmission power however, iscontrolled by the power control of the stronger air link, i.e. by thatbase station which receives the better signal.

[0076] If the radio links in soft handover between the mobile MS1 andthe base stations BS1, BS2 are strongly asymmetric, the transmissionpower of the mobile MS1 may be high enough to reach one of the basestations, i.e. the base station of the stronger cell, it may be not highenough to reach the other base station—the base station of the weakercell(s)—if the radio link is too weak. This implies, that for thesignificantly weaker cell included in the active set, the uplinksynchronization will not be achieved or maintained and the radio linkset up in soft handover will practically fail.

[0077] The invention concerns only soft handover situations in areaswhere the radio link power budget of the radio links to the overlappingcells are imbalanced, Different factors that contribute to the asymmetryare e.g.:

[0078] CPICH E_(c)/I_(o) difference

[0079] CPICH power level difference (e.g. different transmit powers inmicro and macro cells).

[0080] Mast head amplifier used (asymmetric uplink sensitivity).

[0081] Different interference situation due to different cell loads(asymmetric noise rise).

[0082] Difference in required uplink E_(b)N_(o).

[0083] E_(b)=energy per user bit

[0084] N_(o)=interference and noise power density.

[0085] In accordance with the invention, the procedure to automaticallyincrease the transmission power of a mobile station MS1 in soft handoverincludes a first step in which information is detected which indicatesthe radio link power budget of the radio links to the base station BS1of cell C1 and to base station BS2 of cell C2.

[0086] In a second step, this information is used to evaluate a radiolink asymmetry parameter in the overlapping cell area. This parameterindicates the imbalance of the radio links in the overlapping strongercell and weaker cell.

[0087] In a third step, the transmission power of the mobile station MS1is temporarily increased if the asymmetry parameter exceeds a firstthreshold value, this power increase being such that the mobile reachesthe base station of the weaker cell at a level which is sufficient toset up and maintain the uplink synchronization with the respective basestation so that the soft handover will be performed.

[0088] The transmission power of each second type network device MS1 iscontrolled in response to the detected SIR-data of its actual radiolink, these values being compared with a SIR-target provided andactualised by the OLPC-function in the Radio Network Controller.

[0089] In accordance with one embodiment of the invention the asymmetryparameter indicating the imbalance difference of the radio links in theoverlapping stronger cell and weaker cell is calculated a SIR-offsetvalue ASIR which is added to the SIR-target value provided by the outerloop power control at time t₁, i.e. when the second type network deviceenters the soft handover area, cf. FIG. 3. As a consequence ofincreasing the SIR-target value which is forwarded to all first typenetwork devices of the overlapping cells, the transmission power of therespective second type network devices increases simultaneously.

[0090] When the second type network device leaves the soft handover areaat time t₂, the SIR-target value resumes the original value in theuplink OLPC-function of the radio network controller RNC, cf. FIG. 3.The SIR-target value is updated via the dedicated channel frameprotocol.

[0091] As the SIR-target value is the reference value in the fast closedloop control for the transmission power of each second type networkdevice, the increase of the SIR-target value is effected in all basestations involved in the soft handover. then, the closed loop powercontrol automatically adjusts the transmission power of the respectivesecond type network device correspondingly. By this procedure, thetransmission power of the second type network device is increased tosuch a level that the uplink synchronisation with the first type networkdevice, e.g. the base station of the weaker cell is set up and/ormaintained as long as the asymmetric situation is present, i.e. as longas the second type network device is in the overlapping cell area.

[0092] During time t₁ and t₂, i.e. when the second type network deviceenters and leaves the soft handover area, the SIR-target value may—inone alternative embodiment of the invention—also be kept constant duringthe soft handover condition instead of showing the time dependencydetermined by the OLPC-function or assumed to be the minimum SIR-targetvalue.

[0093]FIG. 4 shows the time dependency of the SIR-target value realizedin a second embodiment of the invention. In this embodiment theinvention is implemented by increasing the quality target of thetransport channels within the particular Radio Resource Controlconnection (RRC-connection), i.e. the target bit error rate BER or thetarget block error rate BLER of the respective transport channels arereduced in accordance with the asymmetry parameter evaluated from thedetected asymmetry information.

[0094] The quality target is changed at time t₁, if the second typenetwork device MS1 enters the SHO-area, and the original value of thequality target is resumed at time t₂, i.e. when the soft handoverbetween unbalanced radio links belonging to different cells is over.When increasing the quality target, the uplink OLPC-control functionlocated in the RNC increases the SIR-target value correspondingly, thisincrease being however subject to the time constant of theOLPC-function, so that the SIR-target value increase is slower, cf. FIG.4. This embodiment, if not too slow to cope with quick status changes,allows the SIR-target value to be fully controlled by the OLPC functionin the radio network control during these asymmetric soft handoversituations. The solution may result in a lower SIR-target value in thebase stations participating in the soft handover, thus reducing theuplink interference.

1. A method for controlling the power in an asymmetric soft handovercondition in a communication network, including at least two cells eachcell being served by a first type network device adapted to serve secondtype network devices in the respective cell, the method comprising:temporarily adjusting (step S3) a communication parameter of at leastone second type network device to set up and/or maintain thecommunication of the second type network device with the first typenetwork device of at least one of said cells.
 2. Method according toclaim 1, wherein the communication parameter adjusted in step S3includes the transmission power of the second network device.
 3. Amethod according to claim 1, the method comprising the following steps:detecting information (step S1), said information indicating the linkquality of the links between the second type network device and thefirst type network devices of the cells evaluating an asymmetryparameter in the cell area (step S2) on the basis of the informationgained in the detecting step (S1), said asymmetry parameter indicatingthe imbalance of the link quality in the cells temporarily adjusting thetransmission power of at least one of said second type network devicesin step S3 if the asymmetry parameter evaluated in step S2 exceeds afirst threshold value.
 4. A method according to claim 1, wherein said atleast two cells partly overlap each other, each cell being served by afirst type network device adapted to serve second type network devicesin the respective cell, links in the stronger cell requiring lesstransmission power and in the weaker cell requiring more transmissionpower from the second type network device, the method comprising thefollowing steps: detecting information (step S1), said informationindicating the link quality of the links between the second type networkdevice and the first type network device of the overlapping cellsevaluating an asymmetry parameter in the overlapping cell area (step S2)on the basis of the information gained in the detecting step (S1), saidasymmetry parameter indicating the imbalance of the link quality in theoverlapping cells temporarily increasing the transmission power of saidsecond type network device in step S3 if the second type network devicesenter the overlapping cell area from the stronger cell and if theasymmetry parameter evaluated in step S2 exceeds a first thresholdvalue, to set up and/or maintain an uplink synchronization of the secondtype network device with the first type network device of the weakercell.
 5. A method according to claim 4, wherein the communicationnetwork is a mobile telecommunication network.
 6. A method according toclaim 4, wherein the transmission power of the second type networkdevices are maintained in the adjusting step S3, if the second typenetwork device enters the overlapping cell area from the weaker cell(s).7. A method according to claim 4, wherein the transmission power of thesecond type network device resumes another value when said second typenetwork device leave the overlapping cell area.
 8. A method according toclaim 7, wherein the transmission power of the second type networkdevice resumes the original value which was present before entering theoverlapping area.
 9. A method according to claim 7, wherein thetransmission power of the second type network device resumes a valuenewly determined by power control of the serving cell.
 10. A methodaccording to claim 4, wherein the link quality information in step S1includes the link power budget information.
 11. Method according toclaim 4, wherein the detection step (S1) is adapted to include thedetection of at least one of the following values: CPICH-E_(c)/I_(o)value of the overlapping cells, CPICH power levels of the overlappingcells the uplink sensitivity of the overlapping cells, the differentinterference situation of the overlapping cells due to different cellloads, the difference in required uplink E_(b)/N_(o), wherebyE_(c)=average energy per PN chip for the pilot signal I_(o)=totalreceived power density including signal and interference E_(b)=energyper user bit N_(o)=interference and noise power density.
 12. Methodaccording to claim 4, wherein the detecting step (S1) is adapted toinclude the detection of the SIR-data (signal to interferenceratio-data) for radio links of the second type network device with thefirst type network device of the stronger cell and the weaker cell. 13.Method according to claim 12, wherein an SIR-offset value ΔSIR iscalculated in the evaluation step (S2) on the basis of the informationgained in step S1, the asymmetry parameter corresponding to thisSIR-offset value.
 14. Method according to claim 4, wherein thetransmission power of each second type network device is controlled inresponse to an increased SIR-target value provided and actualised by anouter loop power control (OLPC) and forwarded to the first type networkdevices of the overlapping cells.
 15. Method according to claim 13,wherein the transmission power of said second type network deviceincreases (step S3) by adding the SIR-offset value to the SIR-targetvalue, the resulting new SIR-target value being forwarded to the firsttype network devices of the overlapping cells, the resulting newSIR-target value being kept constant as long as the asymmetry parameterexceeds a pre-given value.
 16. Method according to claim 13, wherein theSIR-offset value is a constant value.
 17. Method according to claim 13,wherein to temporarily increase the transmission power of the secondnetwork device (step S3), the Minimum SIR-target value of the uplinkOuter Loop Power Control function is increased to minimumSIR-target=current SIR-target+ΔSIR, and is forwarded to the first typenetwork devices of the overlapping cells.
 18. Method according to claim15, wherein the SIR-target of the first type network devices resumes theoriginal value when the weaker cell having reduced radio linkconditions, is removed from the active set of cells.
 19. Methodaccording to claim 4, wherein the transmission power of the second typenetwork device is maintained at the increased level as long as thestrong radio link asymmetry evaluated in the evaluation step (S2) existsin the overlapping cell area.
 20. Method according to claim 15, whereinthe SIR target of the first type network devices resumes the originalvalue when the asymmetry parameter evaluated in the evaluation step (S2)decreases below the first threshold value.
 21. Method according to claim15, wherein the SIR-target of the first type network devices resumes theoriginal value when the second type network device leaves theoverlapping cell area.
 22. Method according to claim 15, wherein theSIR-target of the first type network devices resumes a value differentfrom the original value, when the second type network device leaves theoverlapping cell area.
 23. Method according to claim 4, whereinincreasing the transmission power (step S3) includes temporarilyincreasing the quality target of the Outer Loop Power Control means(OLPC function) on the basis of the asymmetry parameter gained in stepS2, as a result of which the Outer Loop Power Control means temporarilyincreases the SIR-target value for the said second type network devicewhich is in soft handover condition.
 24. Method according to claim 23,wherein temporarily increasing the quality target is realized bytemporarily reducing the target Bit Error Rate (BER-target) or thetarget Block Error Rate (BLER-target) for the cells involved inhandover.
 25. Method according to claim 24, resuming the quality targetto the original value when the radio link asymmetry evaluated in step S3is over.
 26. Method according to claim 24, increasing the quality targetof the outer loop power control when the second type network deviceenters the overlapping cell area.
 27. Method according to claim 1,wherein the first type network device is a base station.
 28. Methodaccording to claim 1, wherein the second type network device is a mobilestation.
 29. Method according to claim 4, wherein the mobiletelecommunication network is a wideband code divisional multiple accessnetwork (WCDMA-System).
 30. Device for controlling the power in anasymmetric soft handover condition in a communication network, includingat least two cells each cell being served by a first type network device(BS1, BS2) adapted to serve second type network devices (MS) in therespective cell, the device comprising: additional control means fortemporarily adjusting a communication parameter of at least one secondtype network device to set up and/or maintain the communication of thesecond type network device with the first type network device of atleast one of said cells.
 31. Device according to claim 30, forcontrolling the power in an asymmetric soft handover condition of acommunication network, including at least two cells (C1, C2) partlyoverlapping each other and participating in the soft handover each cellbeing served by a first type network device (BS1, BS2) adapted to servesecond type network devices (MS) in the respective cell, a closed looppower control means controlling the transmission power of each secondtype network device in response to a comparison of the detected SIR-data(signal to interference ratio data) of its actual radio link, with aSIR-target value, an outer loop power control means (OLPC) providing andactualizing the SIR-target value for the closed loop power controlmeans, radio links in the stronger cell (C1) of said cells requiringless transmission power and radio links in the weaker cell (C2)requiring more transmission power from the second type network device,the device comprising the following steps: detection means for detectinginformation, said information indicating the radio link quality of theradio links between the second type network device (MS) and the firsttype network device (BS1, BS2) of the overlapping stronger cell (C1) andweaker cell (C2), respectively evaluation means for evaluating anasymmetry parameter in the overlapping cell area on the basis of theinformation gained from the detecting means, said asymmetry parameterindicating the imbalance of the link quality in the overlapping strongercell (C1) and weaker cell (C2), additional control means for temporarilyincreasing the transmission power of said second type network device ifthe second type network device enters the overlapping cell area from thestronger cell and if the asymmetry parameter evaluated by the evaluationmeans, exceeds a first threshold value, to set up and/or maintain anuplink synchronization with the first type network device of the weakercell (C2).
 32. Device according to claim 31, wherein the link qualityinformation gained by the detection means includes link power budgetinformation.
 33. Device according to claim 31, wherein the additionalcontrol means temporarily maintains the transmission power of saidsecond type network device, if the second type network device enters theoverlapping cell area from the weaker cell.
 34. Device according toclaim 31, wherein the additional control means for increasing thetransmission power of the second type network device (MS) isincorporated in the closed loop power control means and/or the outerloop power control means (OLPC).
 35. Device to claim 31, wherein theadditional control means increases the transmission power of said secondtype network device (MS) only when the second type network device entersthe overlapping cell area.
 36. Device to claim 31, wherein theadditional control means resumes the original value of the transmissionpower of said second type network device when said device leaves theoverlapping cell area.
 37. Device according to claim 31, wherein thetransmission power of the second type network device resumes a valuenewly determined by the power control means of the serving cell, whensaid second type network device leaves the overlapping cell area. 38.Device according to claim 31, wherein the detection means is adapted toinclude the detection of at least one of the following values:CPICH-E_(c)/I₀ value of the overlapping cells, CPICH power leveldifference of the overlapping cells, the uplink sensitivity of theoverlapping cells, the different interference situation of theoverlapping cells due to different cell loads, the difference inrequired uplink E_(b)/N_(o), whereby E_(c)=average energy per PN chipfor the pilot signal I_(o)=total received power density including signaland interference E_(b)=energy per user bit N_(o)=interference and noisepower density.
 39. Device according to claim 31, wherein the detectingmeans is adapted to include the detection of the SIR-data (signal tointerference ratio-data) for radio links of the second type networkdevice (MS) with the first type network device (BS1, BS2) of thestronger cell (C1) and the weaker cell (C2).
 40. Device according toclaim 31, wherein the evaluation means calculates an SIR-offset valueΔSIR on the basis of the information received by the detection means,the asymmetry parameter corresponding to this SIR offset value. 41.Device according to claim 31, wherein an additional control means addsthe SIR-offset value ΔSIR to the SIR-target value provided by the outerloop power control (OLPC) and forwards this new SIR-target value to thefist type network devices of the overlapping cells.
 42. Device accordingto claim 31, wherein an additional control means adds the SIR-offsetvalue ΔSIR to the actual SIR-target value when the second type networkdevice enters the overlapping area and keeps the resulting newSIR-target value constant as long as the asymmetry parameter exceeds apre-given value.
 43. Device according to claim 40, wherein theSIR-offset value is a constant value.
 44. Device according to claim 31,wherein to temporarily increase the transmission power of the secondnetwork device by the additional control means, the minimum SIR-targetvalue of the uplink OLPC function in the radio network controller willbe increased to minimum SIR-target=current SIR-target+ΔSIR, and isforwarded to the first type network device of the overlapping cells. 45.Device according to claim 31, wherein the SIR-target value of the firsttype network devices (BS1, BS2) resumes the original value when theweaker cell (C2) having reduced radio link conditions, is removed fromthe active set of cells.
 46. Device according to claim 31, wherein theSIR-target value of the first type network devices (BS1, BS2) resumes avalue different from the original value, when the weaker cell (C2)having reduced radio link conditions, is removed from the active set ofcells.
 47. Device according to claim 31, wherein the additional controlmeans resumes the SIR target value of the first type network devices tothe original value when the radio link asymmetry evaluated in theevaluation means decreases below the first threshold value.
 48. Deviceaccording to claim 31, wherein the additional control means resumes theSIR-target value of the first type network devices to the original valuewhen the radio link asymmetry decreases below a second threshold valuewhich is smaller than the first threshold value.
 49. Device according toclaim 37, wherein the additional control means resumes the SIR-targetvalue of the first type network devices to the original value when thesecond type network device leaves the overlapping cell area.
 50. Deviceaccording to claim 31, wherein the additional control means isincorporated in the outer loop power control means (OLPC) and/or theclosed control means and increases temporarily the quality target of theouter loop power control means (OLPC function) on the basis of theasymmetry parameter received from the evaluation means, as a result ofwhich the outer loop power control means automatically increases theSIR-target value for the said second type network device which is insoft handover condition.
 51. Device according to claim 50, whereintemporarily increasing the quality target is realized by temporarilyreducing the target Bit Error Rate (BER-target) or the target BlockError Rate (BLER-target) for the cells involved in handover.
 52. Deviceaccording to claim 47, wherein the additional control means resumes thequality target to the original value when the radio link asymmetry isover.
 53. Device according to claim 31, wherein the additional controlmeans increases the quality target of the outer loop power control meanswhen the second type network device enters the overlapping cell area.54. Device according to claim 31, wherein the first type network device(BS1, BS2) is a base station.
 55. Device according to claim 31, whereinthe second type network device (MS) is a mobile station.
 56. Deviceaccording to claim 31, wherein the closed loop power control means isarranged in the first type network devices (BS1, BS2) and wherein theouter loop power control means (OLPC) is arranged in the Radio NetworkController (RNC) of the first type network devices (BS1, BS2). 57.Device according to claim 31, wherein the communication network is amobile telecommunication network.
 58. Device according to claim 31,wherein the mobile telecommunication network is a Wideband Code DivisionMultiple Access Network (WCDMA System).